The present invention is with respect to a peristaltic pump for medical purposes and more specially an enteral pump for artificial feeding with an electric motor and having a flexible pipe element acted upon by a wheel with rollers thereon for peristaltically moving material to be pumped along the pipe element by the rollers on the wheel rolling the element against a rounded backup wall, which is radially spaced from the wheel.
An example of such a peristaltic pump of the prior art may be seen for example in German Offenlegungsschrift specification No. 2,500,463, which has a generally cylindrical housing made in four pieces placed next to each other axially, that is to say a battery part, a middle part for the control systems, a motor part and a pump part next to the side, opposite to the battery part, of the motor part. The wheel with the rollers is, in this respect, normal to the axis of the electric motor and the pipe element for peristaltic pumping purposes is supported on wall parts round the rollers, such wall parts at the same time forming the wall of the cylindrical housing at the end in question.
For a generally rod-like design of the casing of this known peristaltic pump so that the pump, if made with a small overall size, may be taken around by the user with him or her, the diameter of the casing cylinder must be within a certain upper limit. Because the wheel with the rollers on its outer edge has to have a very much smaller diameter than the casing width (because, between the outer side of the casing and the rollers there is to be at least space for the pipe element and the backup wall with its support part) the wheel with the rollers necessarily has to have a very small diameter. The outcome of this is that the peristaltic pipe element has to be positioned in a curve with a generally small diameter round the edge of the small wheel, the wheel then having to be turned at a high speed to get the desired pumping rate. Such a high speed of the wheel with the rollers does, however, make for loud operation, something which is very undesired if the pump is to be taken around by the user all the time with him.
Furthermore there are undesired loading effects on the pipe element which has a very small radius, the working life of the pump then no longer being the 4000 to 5000 hours as a possible lower limit, but lower values. Lastly, the pumping function is likely to be second rate because the rollers operate against a body with a small diameter and, for this reason, there is a small spacing between the rollers, so that they are only in a position of peristaltically pumping a small amount of material between the nips between the rollers and the pipe element.
Because furthermore the wheel with the rollers thereon is fixed on the shaft of the driving motor, quite in addition to the limited amount of space on hand in the pump, a small diameter of the wheel is necessary because the speed of the motor is to be stepped down to the speed of the wheel in a single stage of gearing. Furthermore, with a small wheel diameter, the speed of the motor has to be decreased to values, which for an electric motor, are very low, for pumping at low rates. Such low motor speeds are in fact only possible with high-price special-purpose motors. Normal battery powered DC motors may not be used because they have a starting speed of about 100 rpm, this being not nearly low enough for pumping at the desired low speed, in view of the small diameter of the wheel.
Although it would be possible to have step-down gearing with coaxial input and output shafts between the shaft for driving the wheel with the rollers on the one hand and the shaft of the electric motor on the other, such gearing being for example in the form of an epicyclic system so as to give the desired step-down ratio, such a system is complex and likely to be the cause of trouble conditions. Furthermore, for using such gearing, an axial overall size of the pump would be increased because the pump part, the motor part, the control part and the battery part would have to be put one after the other in line.
On the other hand, one purpose of the present invention is that of designing a peristaltic pump of the sort noted making a flat, compact mechanical design possible without any undesired limits on the diameter of the wheel with the rollers.
For effecting this purpose, and further purposes, the axis of turning of the wheel is normal to the axis of the electric motor.
Because of the axis of the wheel being normal to that of the electric motor, the width of the wheel (its largest dimension) is parallel to the direction of the length of the electric motor, this length being the greatest dimension thereof. In a direction normal to these main dimensions it is then, for this reason, only necessary to have space for the thickness of the wheel and the thickness or the diameter of the electric motor. Separately from the question of the diameter of the wheel, a very flat design is produced so that the peristaltic pump's casing may be generally flat and rectangular, it resting flatly against the body of the user and hardly being seen if at all. The breadth of the housing is, in comparison with its thickness, hardly important so that, with respect to the diameter of the wheel with the rollers, on which the width of the housing is generally dependent, there are no further conditions to be kept to with respect to the size of the unit. For this reason, a generally large-diameter wheel with the rollers may be used without any undesired effects. With such a size of wheel, a desired pumping rate may be produced with the wheel turning at a low speed. A further outcome of this design is that the pump will be quiet in operation with exact rate control and, if the casing is block-like or rectangular, it will be possible to have room for batteries or the like on the two sides of the electric motor within the corners of the casing, such corners being otherwise empty because the wheel with the rollers is round and not rectangular. Putting it differently, the batteries or the like take up space which would not otherwise be used and do not have to be put in special parts of the casing which would make it broader or longer. Because the axes of the wheel with the rollers and of the electric motor are normal to each other, the gearing therebetween may have a very high step-down ratio of at least 1:100 and more specially more then 1:500 using a simple pinion keyed on the electric motor's shaft and running against teeth on the outer edge of the wheel. For this reason, the step-down gearing does not take up any further space.
Specially useful effects are produced if the wall supporting the pipe element against the rollers is united with a support part which may be moved in the direction of the force produced by the wheel on the pipe element, the backup wall being spring-loaded so as to be forced springingly towards the rollers on the wheel, in the way detailed in German patent application P No. 31 14 128.5 of the same applicant of even date and in U.S. application made on the same date as the present application naming the same assignee.
Useful further development of the invention will be seen in the dependent claims.